Due to small power batteries in WSNs, efficient utilization of battery power is an important factor. Clustering is an efficient technique to extend life time of sensor networks by reducing the energy consumption. Many clustering techniques were introduced to find cluster heads in a cluster. One of them which is Stable election protocol. SEP protocol is for clustered heterogeneous wireless sensor networks. SEP is based on weighted election probabilities of each node to become cluster head according to the remaining energy in each node. In this project, implementation of SEP is done. This project also concludes by studying the sensitivity of our SEP protocol to heterogeneity parameters capturing energy imbalance in the network. The analysis show that SEP yields longer stability region for higher values of extra energy brought by more powerful nodes.